West Ham are leading the chase to sign Lyon centre-back Samuel Umtiti, Sky sources understand.
The Cameroon-born France Under-21 international made 30 appearances for Lyon last season and is regarded as one of Europe's brightest young talents.
Umtiti has previously been linked with moves to Paris Saint-Germain, Barcelona and Spurs.
France manager Didier Deschamps has named the 22-year-old on the standby list for this summer's European Championship.
The news of West Ham's efforts to sign Umtiti comes on the same day news emerged of a bid from the Hammers for AC Milan's Colombian striker Carlos Bacca.
West Ham have already had bids for Alexandre Lacazette and Callum Wilson turned down this summer, but co-chairman David Sullivan told Sky Sports News HQ last week the club are keen to add a world-class goalscorer to their ranks.
West Ham have already agreed a deal to sign Norway international Havard Nordtveit, who will join the club on a free transfer following the expiry of his contract with German side Borussia Monchengladbach.